Slit-slide-sew bijections for constellations and quasiconstellations

Jérémie Bettinelli (1, 2, 3, 4) , Dimitri Korkotashvili (1, 3)

1 IP Paris - Institut Polytechnique de Paris
2 CNRS - Centre National de la Recherche Scientifique
3 X - École polytechnique
4 LIX - Laboratoire d'informatique de l'École polytechnique [Palaiseau]

We extend so-called slit-slide-sew bijections to constellations and quasiconstellations. We present an involution on the set of hypermaps given with an orientation, one distinguished corner, and one distinguished edge leading away from the corner while oriented in the given orientation. This involution reverts the orientation, exchanges the distinguished corner with the distinguished edge in some sense, slightly modifying the degrees of the incident faces in passing, while keeping all the other faces intact. The construction consists in building a canonical path from the distinguished elements, slitting the map along it, and sewing back after sliding by one unit along the path. The involution specializes into a bijection interpreting combinatorial identities linking the numbers of constellations or quasiconstellations with a given face degree distribution, where the degree distributions differ by one $+1$ and one $-1$. In particular, this allows to recover the counting formula for constellations or quasiconstellations with a given face degree distribution. Our bijections furthermore provide an algorithm for sampling a hypermap uniformly distributed among constellations or quasiconstellations with prescribed face degrees.

Mots clés: bijection; plane map; hypermap; constellation; map enumeration

Domaines: Mathématiques [math]; Informatique [cs]

Jérémie Bettinelli, Dimitri Korkotashvili. Slit-slide-sew bijections for constellations and quasiconstellations. 2023. ⟨hal-04299507⟩